Non-contact tool setting apparatus and method for moving tool along tool inspection path

ABSTRACT

A method for assessing the profile of a tool using a non-contact tool setting apparatus that includes a transmitter for emitting a light beam and a receiver for receiving the beam. The receiver generates a beam intensity signal describing the intensity of received light. The setting apparatus is mounted to a coordinate positioning apparatus that allows the tool to be moved relative to the setting apparatus. The method includes using the coordinate positioning apparatus to move the tool relative to the setting apparatus along a tool inspection path, the tool inspection path being selected so that the light beam is traced substantially along a periphery of the tool to be inspected. Beam intensity data is collected describing the beam intensity signal that is generated by the receiver as the tool inspection path is traversed and analysis of the collected beam intensity data is used to assess the tool profile.

This application is a Continuation Application of U.S. patentapplication Ser. No. 16/635,135, filed Jan. 29, 2020, which is aNational Stage Entry of PCT/GB2018/052472, filed Aug. 31, 2018, whichclaims priority to European Patent Application No. EP 17189504.8, filedSep. 5, 2017. The entire contents of those prior applications areincorporated by reference herein in their entireties.

The present invention relates to non-contact tool setting apparatus forcoordinate positioning apparatus and particularly to an improved methodand apparatus for measuring the profile of a tool.

Break-beam tool setting devices for use on machine tools are known, forexample see U.S. Pat. No. 6,496,273. Tool setting apparatus of this typeincludes a light source which generates a beam of light which is passedto a light detector. During a tool setting operation, the machine toolis operated to move a tool into and out of the light beam. Interruptionof the light beam by the tool is detected by analysis of the detectoroutput signal and the apparatus generates a so-called “trigger signal”to indicate to the associated machine tool that the light beam has beenbroken. Typically, this trigger signal is issued when the light levelreaches 50% of the “beam clear” state (i.e. when 50% of the optical beamis blocked from reaching the detector). The machine tool records theposition of the tool relative to the tool setting device on receipt ofthe “trigger signal” thereby allowing a single position on the tool edgeto be determined. This measurement move may be repeated multiple timesto measure, one by one, multiple different positions on the tool edge.This arrangement thus allows tool size, such as the tool length and/ortool diameter, to be measured.

EP1587648 describes an alternative way of generating a “trigger signal”during a measurement move in which a rotating or non-rotating tool ismoved into or out of a light beam. In particular, EP1587648 describesdigitising a detector output signal and identifying minima and/or maximain the digitised data that correspond to one or more teeth of thecutting tool entering and/or exiting the beam during the measurementmove. A digital processor determines, in real-time, whether theminima/maxima conform to a curve of expected type and issues a triggersignal only when such a fitted curve crosses a threshold. In thismanner, it is possible to measure the position of a single point on thetool during a measurement move into, or out of them the light beam. Fora stationary tool, the measured position is on the edge that blocks thelight beam. For a rotating tool having multiple cutting teeth that arerotated into and out of the beam, the measured position is on thecutting edge having the largest diameter.

The above described tool setting devices thus allow the position of apoint on the edge of a tool to be established relatively quickly thusproviding a measure of tool length or tool diameter. It is also possibleto measure the profile of a tool by repeating the measurement move so asto measure multiple different points along the edge of the tool, butsuch a process can be very time consuming (i.e. the tool has to be movedinto and out of the beam multiple times) and is typically consideredimpractical. More details of such a prior art tool measurement processare described below with reference to FIG. 9 a.

According to a first aspect of the present invention, there is provideda method for assessing the profile of a tool using a non-contact toolsetting apparatus comprising a transmitter for emitting a light beam anda receiver for receiving the light beam, the receiver generating a beamintensity signal describing the intensity of received light, thenon-contact tool setting apparatus being mounted to a coordinatepositioning apparatus that allows the tool to be moved relative to thenon-contact tool setting apparatus, the method comprising the steps of;

-   -   (i) using the coordinate positioning apparatus to move the tool        relative to the non-contact tool setting apparatus along a tool        inspection path, the tool inspection path being selected so that        the light beam is traced substantially along a periphery of the        tool to be inspected,    -   (ii) collecting beam intensity data describing the beam        intensity signal that is generated by the receiver as the tool        inspection path of step (i) is traversed, and    -   (iii) analysing the beam intensity data collected in step (ii)        to assess the tool profile.

The first aspect of the present invention thus relates to a method forassessing the profile of a tool using a non-contact tool settingapparatus. The profile that is assessed may be the shape, position ordimension(s) of one or more cutting features of the tool. Thenon-contact tool setting apparatus comprises a break-beam type tooldetection system in which a light beam (e.g. a laser beam) emitted fromthe transmitter (e.g. by a laser diode of the transmitter) is passedthrough a region of free space to the receiver. The receiver detects(e.g. using a photodiode) the received light and generates a beamintensity signal describing the intensity of the received light. Thenon-contact tool setting apparatus is mounted to a coordinatepositioning apparatus, such as a machine tool, that can be programmed tomove the tool relative to the non-contact tool setting apparatus. Therelative motion may be imparted by moving the tool and/or thenon-contact tool setting apparatus.

The method of the present invention comprises a step (i) of using thecoordinate positioning apparatus to impart relative motion between thelight beam and the tool to define a tool inspection path. In particular,step (i) comprises moving the tool relative to the non-contact toolsetting apparatus so that the light beam is traced along a periphery ofthe tool. The coordinate positioning apparatus is thus arranged to movethe light beam along a tool inspection path that causes the light beamto be scanned along a periphery of the tool. In other words, the toolinspection path is selected so that the light beam is moved in adirection that is approximately tangential to the periphery of the tool.This should be contrasted to the prior art techniques described above inwhich the tool is moved into or out of the light beam (i.e. in adirection substantially perpendicular to the edge of the tool) toacquire a measurement point.

For a non-rotating (stationary) tool the periphery of the tool is simplythe edge of the tool that is to be inspected. If the tool is rotating,the tool inspection path is set to trace the light beam along theoutermost extent of the multiple edges of the rotating tool. The motionthat traces the light beam along the periphery of the tool is thusperformed in addition to any rotary tool motion (e.g. rotation of thetool about its longitudinal axis) that also causes different parts ofthe tool circumference to be rotated into and out of the light beam. Themotion that traces the light beam along the periphery of the tool ispreferably only linear (translational) motion and does not include anyrotational motion. In other words, the tool inspection path preferablydefines only linear motion (e.g. motion along mutually orthogonal x, yand/or z axes) of the tool relative to the light beam. The toolinspection path may, depending on the shape of the tool, be a straightline and/or it may include one or more curved sections to follow theperiphery of a curved tool. The tool inspection path may pass along onlyparts of the tool that are to be measured or it may pass around thewhole periphery of the tool. Preferably, at least some of the light beamfalls on the tool for the duration of the traverse of the toolinspection path. As explained below, the tool inspection path mayinclude a single pass around the tool periphery, or it may includemultiple passes around the tool periphery.

Step (ii) comprises sampling the beam intensity signal that is generatedas the tool inspection path is traversed and thereby generating beamintensity data. For example, the beam intensity signal may be digitisedby an analogue-to-digital converter to generate the set of beamintensity data. In other words, the beam intensity signal that describesthe level of beam obscuration will typically vary as the tool inspectionpath is traversed. Step (ii) comprises periodically sampling the beamintensity signal to generate the beam intensity data that are to beanalysed. Any suitable sampling rate may be used. For example, a highersampling rate may be used for rotating tools (e.g. to obtain beamintensity data describing beam obscuration as the tool is rotated). Thesampling rate may be varied as the light beam traverses the toolinspection path to allow more beam intensity data to be collected forcertain regions of the tool. It should also be noted that the light beammay traverse the tool inspection path at a single, constant, speed or itmay be moved at different speeds when passing along different parts ofthe tool inspection path. There may also be one or more dwell periodsdefined as part of the tool inspection path in which the light beam isnot moved relative to the tool (although the tool itself may still berotating during any such dwell period). Beam intensity data collectedduring such a dwell period is particularly useful when measuringrotating tools (e.g. to allow position at multiple points around thetool circumference, such as the edges of different cutting teeth, to bemeasured). It is also possible to obtain more accurate information fromthe coordinate positioning apparatus about tool position relative to thenon-contact tool setter during such a dwell period.

As described below, the collected beam intensity data includesinformation on the profile of the tool. Step (iii) thus comprisesanalysing the beam intensity data, using any one of the techniquesdescribed below. The analysis may comprise analysing all of thecollected beam intensity data or it may comprise selecting a subset ofthe data (e.g. from a region or regions of interest along the toolinspection path). In this manner, the tool profile can be assessed.

The present invention thus provides a quick and simple technique formeasuring the profile of a tool. Instead of individually measuringmultiple points around a tool by repeatedly driving the tool into andout of the light beam as per the touch trigger type measurementsdescribed above, the periphery of the tool can be measured in detail viaa scanning type operation that traces the light beam around the toolperiphery. This makes the tool profiling process quicker and easier.

Advantageously, the tool inspection path is selected so that the lightbeam traces a path along the nominal position of the tool periphery. Inother words, the tool inspection path may be generated using knowledgeof the nominal or expected tool profile. For example, the toolinspection path may be generated from tool design (e.g. CAD) data of thetool. The tool inspection path may be selected so that, for a tool thatconforms to its nominal specification, the light beam is obscured by acertain pre-set level (e.g. 50%) as it traverses the tool inspectionpath. Any deviation in beam intensity data from the pre-set level thusindicates the tool profile deviates from nominal. Step (iii) may thuscomprise assessing whether the collected beam intensity data correspondsto that expected if the profile of the tool being inspected conformed toits nominal profile. Any deviation greater than a certain amount may beused to indicate required tool tolerances are not met. Alternatively,the deviation could be used to adjust the assumed dimensions of thetool.

As explained above, any deviation in beam intensity data from a pre-setlevel (e.g. from the 50% level) can be used to indicate the tool profiledeviates from nominal. A calibration process could also be performedprior to measurement to ascertain the change in the beam intensitysignal that will occur when there is a certain shift in the location ofthe tool edge within the light beam. For example, a calibration table orfunction could be generated that describes the relationship between thetool edge position within the beam and the beam intensity signal. Itshould be noted that the relationship between the tool edge position andthe beam intensity signal may be non-linear, especially for largerchanges in position within the beam. Such a calibration process could,for example, involve moving a tool edge away from the position thatresults in 50% beam occlusion in small steps (e.g. 10 μm step) andrecording the resulting beam intensity signal at each position. Thistype of calibration would allow any changes in the beam intensity signal(e.g. a shift from 50% to 60% or from 50% to 40%) to be converted into adeviation or shift in tool edge position. In this manner, the assumeddimensions of the tool could be adjusted based on the acquiredmeasurements.

Advantageously, step (iii) comprises comparing the beam intensity datacollected in step (ii) with previously acquired beam intensity data. Thecomparison may be a direct comparison of individual beam intensity datavalues. Alternatively, an indirect comparison may be performed (e.g. ofthe minima intensity values for rotating tools that are describedbelow). Conveniently, the previously acquired beam intensity datacomprises data collected from a previous measurement of the same tool.For example, the previously acquired beam intensity data may becollected prior to the tool being used for cutting purposes.Alternatively, the previously acquired beam intensity data may comprisedata collected from a measurement of a reference tool having the samenominal profile as the tool. In other words, a “golden” or referencetool that is nominally identical to the tool being measured may providethe reference or baseline measurements with which the beam intensitydata collected in step (ii) are compared. Step (iii) may thusconveniently provide an indication of whether the tool profile haschanged relative to the previous measurement. This may includeindicating if any critical sections of the tool profile have changed bymore than an amount that might result in the cutting performance beingcompromised. The indication may thus comprise raising an error flag whencertain tool profile changes have occurred.

The method may be performed using a tool that is not being rotated (i.e.the only motion during measurement may be the motion of the toolrelative to the light beam along the tool inspection path).Alternatively, the tool may be rotated during measurement. The tool maythus be held in a rotatable spindle of the coordinate positioningapparatus. The tool may comprise one or more cutting teeth locatedaround its radius. Conveniently, the tool is rotated about itslongitudinal axis whilst it is moved along the tool inspection path. Inthis manner, the different cutting teeth move into and out of the lightbeam in turn during rotation of the tool producing minima and/or maximain the beam intensity data. Step (iii) may thus conveniently compriseidentifying minima and/or maxima in the beam intensity data. Theidentification of such minima and/or maxima may be performed by adigital signal processing method of the type described in EP1587648.

Advantageously, the tool comprises a plurality of cutting teeth.Conveniently, step (iii) comprises identifying the minima and/or maximaassociated with each tooth of the tool. In this manner, it is possibleto separately assess the profile of each tooth. For example, thevariation in the minima and/or maxima associated with a tooth thatoccurs as the tool inspection path is traversed may be used to assessthe profile of that tooth. This allows separate profiling of differentteeth of a rotating tool to be performed with a single traverse of thetool inspection path. For example, size deviations of individual teethcould be determined using previously acquired calibration data asdescribed above or any such deviations could be compared to previousmeasurements. In addition to identifying minima and/or maxima, the shapeof the minima and/or maxima may be used to infer certain tool profileinformation. Step (iii) may thus comprise analysing the shape of theminima and/or maxima to assess the profile of the tooth producing theminima and/or maxima.

Advantageously, step (ii) comprises digitising the beam intensity signalto generate the beam intensity data. This may be performed using ananalogue to digital converter (ADC) to sample the beam intensity signal.A sampling rate of at least 10 kHz is preferably used (e.g. for a toolrotating at 3000 rpm). Conveniently, a sampling rate of at least 100 kHzis used. A sampling frequency of between 100 KHz and 500 kHz mayusefully be employed. Step (iii) advantageously comprises using adigital signal processor (DSP) to analyse the beam intensity data. Thismay be done after all the data has been collected, or the analysis maybe started when the data is still being collected. As mentioned above, aconstant sampling rate may be used. Alternatively, the sampling rate maybe varied as the tool inspection path is traversed.

The tool inspection path may be pre-calculated prior to the coordinatepositioning apparatus moving the tool. In other words, the toolinspection path may comprise a pre-programmed path that the coordinatepositioning apparatus is programmed to follow prior to starting step(i). Instead of such a known-path technique, the tool inspection pathcould be generated during step (i) using feedback passed from thenon-contact tool setting apparatus to the coordinate positioningapparatus. For example, the tool inspection path could be selected tomaintain the beam intensity signal within a certain range.

Any suitable coordinate positioning apparatus may be used to implementthe present method. Advantageously, the coordinate positioning apparatusis a machine tool (e.g. a computer numerically controlled or CNC machinetool). Alternatively, the coordinate positioning apparatus may be acoordinate measuring machine (CMM), a flexible gauge (such as theEquator system sold by Renishaw plc, Wotton-Under-Edge, UK) or anoffline tool inspection apparatus etc.

The non-contact tool setting apparatus used in the method may comprisediscrete transmitter and receiver units that can each be attached to abracket. Alternatively, a single unit may be provided that comprises thetransmitter and receiver. The apparatus may include an interfaceseparate to the transmitter/receiver unit(s) or the interface may beformed integrally with such units. A processor may be provided toperform step (iii) of the method. An ADC may be provided to perform step(ii). The processor and/or ADC may be located in the interface, in aseparate processing unit or be provided as part of the coordinatepositioning apparatus.

Advantageously, the transmitter comprises a laser for generating light.The transmitter may also comprise optics for providing a collimatedlight beam. Alternatively, the transmitter may provide a focused (ratherthan collimated) laser beam. The light beam may have a substantiallyelliptical or circular profile (e.g. a Gaussian beam profile). The lightbeam may have a diameter of less than 0.5 mm, less than 1 mm, less than2 mm or less than 3 mm.

A second aspect of the present invention comprises apparatus forperforming non-contact tool profile measurement on a coordinatepositioning apparatus, the apparatus comprising; a transmitter foremitting a light beam, a receiver for receiving the light beam andgenerating a beam intensity signal describing the intensity of lightreceived at the receiver, an analogue-to-digital converter for producingbeam intensity data from the beam intensity signal, and a processor foranalysing the beam intensity data, characterised in that the processoris configured to assess the profile of a tool by analysing the beamintensity data produced when the tool is moved along a tool inspectionpath, the tool inspection path being selected to trace the light beamaround the periphery of the tool. The apparatus may include any one ormore features described above in the context of the analogous method.

According to a third aspect of the invention, there is provided a methodof measuring a tool using a non-contact tool setting apparatuscomprising a transmitter for emitting a light beam and a receiver forreceiving the light beam, the receiver generating a beam intensitysignal describing the intensity of received light, the non-contact toolsetting apparatus being mounted to a coordinate positioning apparatusthat allows the tool to be moved relative to the non-contact toolsetting apparatus, the method comprising the steps of; (i) using thecoordinate positioning apparatus to move the tool through the lightbeam, and (ii) collecting beam intensity data describing the beamintensity signal that is generated by the receiver during step (i),characterised by a step (iii) of comparing the beam intensity datacollected in step (ii) to previously acquired beam intensity data, thecomparison providing an indication of whether the profile of the toolhas changed. Step (i) may comprise moving the tool along a toolinspection path and the previously acquired beam intensity data may havebeen created by moving the tool along the same inspection path.

The invention will now be described, by way of example only, withreference to the accompanying drawings, in which;

FIG. 1 shows a non-contact tool setting apparatus of the presentinvention,

FIG. 2 shows a cutting tool with a light beam moved along its periphery,

FIG. 3 shows the beam intensity data collected as the path shown in FIG.2 is traversed,

FIG. 4 shows a multi-tooth cutting tool that is rotated whilst a lightbeam is moved along an inspection path along its periphery,

FIG. 5 shows the beam intensity data collected as the path shown in FIG.4 is traversed,

FIG. 6 shows the intensity minima associated with the different teeth ofthe tool shown in FIG. 5 plotted as a function of the position along theinspection path,

FIG. 7 shows the intensity minima curve plotted against a previousmeasurement of the same tool,

FIG. 8 shows how a camera could be used to photograph any identifiedtool defects,

FIG. 9a illustrates a prior art tool inspection process, and

FIGS. 9b and 9c illustrate tool periphery scanning of the presentinvention.

Referring to FIG. 1, a tool setting apparatus of the present inventionis illustrated. The apparatus comprises a transmitter 10 for generatinga substantially collimated beam of light 12. The transmitter 10 includesa laser diode and suitable optics (not shown) for generating thecollimated beam of light 12. A receiver 14 is also illustrated forreceiving the beam of light 12. The receiver comprises a photodiode (notshown) for detecting the beam of light 12.

The transmitter 10 and receiver 14 are both affixed to a common base 20by pillars 18. This arrangement ensures the transmitter 10 and receiver14 maintain a fixed spacing and orientation relative to one another. Thebase 20 may then be mounted directly to the bed, or indeed anyappropriate part, of a machine tool. It should also be noted thatvarious alternative structures for mounting the transmitter and receivercould be used. For example, a common housing for the transmitter andreceiver could be provided or discrete transmitter and receiver unitscould be separately mounted to the machine tool.

The apparatus also comprises an interface 15 connected to thetransmitter 10 and receiver 14 via electrical cables 17. The interface15 provides electrical power to the transmitter 10 and receiver 14 andalso receives a beam intensity signal from the photodiode detector ofthe receiver 14. The interface 15 comprises an analogue to digitalconvertor (ADC) 18 that samples the analogue beam intensity signalgenerated by the receiver 14 and generates a stream of digital beamintensity values. This stream of digital beam intensity values, alsotermed beam intensity data, are passed to a digital signal processor(DSP) 20 for analysis. The results of the analysis may be passed to themachine tool 30 via link 28. In this example, the ADC 18 and DSP 20 areprovided in the interface 15 but they could be included in any part ofthe system (e.g. in the receiver, machine tool controller etc). Thusfar, the apparatus is analogous to that described in EP1587648.

Referring next to FIGS. 2 and 3, the tool profile assessment techniqueof the present invention will be described for a non-rotating tool. FIG.2 illustrates a cutting tool 50 that comprises a cutting edge 52. Thecutting tool has a nominal tool profile and is held by the moveablespindle of the machine tool (not shown). The location of the cuttingtool and the location of the tool setting apparatus within the machinetool are known and the machine tool can be programmed to move thecutting tool 50 relative to the tool setting device.

In use, the machine tool is configured to move the tool so the lightbeam initially impinges on a first point 54 on the tool periphery. Inthis initial location, approximately fifty percent of the light beam isobscured. The tool is then moved so that the light beam traces the toolinspection path (as indicated by the pair of dashed lines 56) around thetool periphery until it reaches the second point 58. It can be seen thatmotion along the tool inspection path is substantially tangential to thetool periphery. During the movement of the beam along the toolinspection path 56, the beam intensity data generated by the ADC 18 ofthe tool setter device from the beam intensity signal is collected andstored.

Referring next to FIG. 3, the beam intensity data 60 is plotted as afunction of the position P along the tool inspection path. If themachine tool moves the tool at a constant speed, then the relativeposition along the tool inspection path can simply be inferred from thetime of acquisition of the beam intensity data. FIG. 3 also shows thenominal or predicted beam intensity data 62 that would be expected if atool of nominal dimensions was moved along the same tool inspectionpath. The difference between the collected beam intensity data 60 andthe predicted beam intensity data 62 provide a measure of how much thetool 50 deviates from its nominal size and shape.

Referring next to FIG. 4, a rotatable cutting tool 80 is illustratedthat has four cutting teeth. It should be noted that the three teeth 82a, 82 b and 82 c are shown in solid outline whilst the fourth tooth 82d, which is located on the rear face of the tool shaft in theorientation illustrated in FIG. 4, is shown in dashed outline. The tool80 is measured whilst it is being rotated about its longitudinal axis Rby the machine tool spindle in which it is retained. The light beam istraced around the periphery of the tool along the tool inspection path.In particular, the tool inspection path extends around the periphery ofthe tool from the first point 84 to the second point 86. The spatialextent of the light beam as it traverses the path is illustrated by thedashed lines 88. During the movement of the beam along the toolinspection path, the beam intensity data generated by the ADC 18 of thetool setter device is collected and stored.

FIG. 5 illustrates some of the beam intensity data collected duringinspection of the tool described with reference to FIG. 4. The beamintensity data is plotted as a function of the position P along the toolinspection path. Again, this position may be inferred from the time ofdata collection if the path is traversed at constant speed. The tool isrotating during the measurement and hence the beam intensity dataincludes minima that occur when each one of the four cutting teethfurther occlude the beam. The series of minima are generated by each ofthe four teeth in turn as they rotate into the beam. The minima labelleda, b, c, and d in FIG. 5 thus correspond to the beam occlusion obtainedwhen each of the four different cutting teeth 82 a-d respectivelyocclude the beam. The minima may be identified by the DSP 20 using anyof the techniques described in EP1587648. Furthermore, the DSP 20 can beconfigured to separate out the minimum values that are obtained from thedifferent teeth of the cutting tool.

FIG. 6 shows the beam intensity at each identified minima, plotted as afunction of position along the tool inspection path. In particular,curves 90 a, 90 b, 90 c and 90 d show the minima arising from the teeth82 a, 82 b, 82 c and 82 d respectively. It should be noted that only avery small amount of the collected beam intensity data (i.e. datacollected during three rotations of the tool) is shown in FIG. 5 andthat the curves of FIG. 6 are generated from a large number of suchminima. Curves 90 a, 90 b, 90 c and 90 d thus show the extent that eachof the four different teeth 82 a, 82 b, 82 c and 82 d of the cuttingtool occlude the light beam as the tool inspection path is traversed bythe rotating tool.

The data plotted in FIG. 6 allows any chips or build-up of material onthe teeth of the cutting tool to be identified. In particular, the peak92 in curve 90 d shows there is a chip in the tooth 82 d of the tool;this peak 92 results from the intensity of the minima associated withtooth 82 d increasing due to the chip allowing more light to pass to thereceiver. Similarly, the trough 94 in curve 90 c shows a build-up ofexcess material on the tooth 82 c; this trough 94 results from theintensity of the minima associated with tooth 82 c decreasing furtherdue to the excess material blocking more light. Furthermore, thelocation of the defect (e.g. the chip or excess material) on each toothcan be determined from the position P of the peak and/or trough alongthe tool inspection path.

The minima shown in FIG. 6 will alone allow the presence and position ofdefects to be determined. As shown in FIG. 7, it is also possible tocompare a plot of minima values measured for a certain tool topreviously acquired minima data for that tool. In particular, theprocess of determining the intensity of certain identified minima as afunction of position along the tool inspection path can be repeatedmultiple times. For example, such minima data may be collected from atool prior to use of that tool for cutting purposes. A reference curve100 can thus be obtained that provides information on the profile of theunused tool. After the tool has been used for a cutting operation, themeasurement process can be repeated using the same tool inspection path.A minima value curve 102 can then be generated and compared to thereference curve 100. Any differences between the curve indicates wear ofthe cutting surface and any chips or build-up of material can also beidentified from the differences between the curve 102 and the referencecurve 100. A difference plot (i.e. curve 100 minus curve 102 or viceversa) may be used to provide a visual indication of any differencesthat are present.

Referring to FIG. 8, the addition of a camera for visually inspecting atool is described. In particular, FIG. 8 shows a tool setting apparatus150 of the type described above that emits a light beam 152 and ismounted to the bed 160 of a machine tool. The tool setting apparatus 150is arranged to inspect a tool 170 held by a spindle 172 of the machinetool when that tool is located in the region 174 of the light beam 152.As described above, the tool setting apparatus 150 allows defects 188 inthe tool 170 to be identified and in particular it permits the positionof such defects on a tool to be determined. In addition to the toolsetting apparatus 150, a front lit camera system 180 is also provided.The camera system emits a white light beam 182 and can take images ofany objects located within its field of view 184. The location of thefield of view 184 is known relative to the tool setting apparatus 150;i.e. they are separated by the positional difference V.

In use, the tool setting apparatus 150 is used to identify defects 188on the tool 170. The positions of the tool setting apparatus 150, thecamera's field of view 184 and the tool 170 are all known in thecoordinate system of the machine tool. This means that the machine toolcan move the spindle 172 so that the defect 188 on the tool 170 that hasbeen identified by the tool setting apparatus 150 can be placed in thefield of view 184 of the camera system 180. This allows an image of thetool defect to be captured, which in turn can allow an operator toassess the nature of the detected defect. Although the tool settingapparatus 150 is preferably of the type described above, it couldcomprise any tool setting apparatus.

For completeness, a detailed comparison of prior art tool settingtechniques to the technique of the present invention will be given withreference to FIGS. 9a-9c

Referring to FIG. 9a , a prior art tool measurement process isillustrated. As explained in the introduction above, the light beam of aprior art non-contact tool setter is moved towards a tool 202 from aninitial position 204 spaced apart from the tool 202. In practise, thelight beam is usually stationary and the tool is moved into the beam,but the same relative motion occurs as if the light beam was beingmoved. The light beam thus moves along a path that is substantiallyperpendicular to the edge of the tool 202 to be measured. In FIG. 9a ,the light beam is initially at a start position 204. At the point 206when the tool 202 obscures 50% of the light beam, a trigger signal isissued by the non-contact tool setter. The machine tool receives thetrigger signal and records the position at which the trigger eventoccurred. This allows the position of a single point 208 on the surfaceof the tool 202 to be determined. This process may be repeated tomeasure multiple points on the tool edge.

FIG. 9b show a tool measurement process according to the presentinvention. As described above, the light beam is directed to a startposition 222 on the edge of the tool. In this example, a tool of nominaldimensions will obscure approximately fifty percent of the light beam.The light beam is then traced along the peripheral edge of the tool fromthe start position 222 to an end position 224 (the path followed by thelight beam is the so-called tool inspection path). At multiple points226 along the tool inspection path, beam intensity data are collected.The tool inspection path may be traced in a continuous motion (e.g. atconstant speed) or the speed may be varied as the path is traversed. Itis also possible to dwell at each of the points 226 (i.e. momentarilyhalt the motion of the light beam relative to the tool) and tooptionally perform an averaging procedure at each point (e.g. to improvethe signal-to-noise ratio of the beam intensity data and/or to obtain amore accurate measurement of the position of the tool relative to thenon-contact tool setter).

For a perfect tool (i.e. a tool that corresponds exactly to the nominaltool profile) there will be (in this example) fifty percent of the lightbeam obscured at each point along the tool inspection path. For anactual tool (which may have become worn or experienced material build-upduring a machining operation) any local deviations in the tool edgeposition will result in the amount of the light beam that is obscuredbeing different to the fifty percent level expected for a nominal tool.In other words, deviations in the beam intensity data from the expectedfifty percent at each of the points 226 indicates the tool is larger(obscuring more of the light beam) or smaller (obscuring less of thelight beam) than expected. The beam intensity data are combined withinformation from the machine tool describing the position of the lightbeam 220 at each point 226 to provide multiple measurements of thesurface position of the tool. In this manner, multiple points 226 can bemeasured in a rapid scanning-type action without a need to move the toolback-and-forth into the beam as per the prior art technique illustratedin FIG. 9 a.

Referring to FIG. 9c , it is noted that the tool inspection path maycomprise multiple traverses along the peripheral edge of the tool. Thismay be done, for example, if the uncertainly in the nominal location ofthe tool edge is significantly greater than the width of the light beam.

FIG. 9c shows a tool inspection path in which a light beam is movedlinearly downwards from an initial position 250 to a first position 252.The light beam is then stepped sideways to a second position 254 beforebeing moved linearly upwards to the third position 256. It is thenstepped sideways to a fourth position 258 before being moved linearlydownwards to an end position 260. Although the linear move between thesecond position 254 and third position 256 alone is sufficient tomeasure the edge of a tool 264 in a nominal location, it would not beable to measure a tool shifted from that nominal location by more thanthe beam width (e.g. to the tool position indicated by the dashedoutline tool 266). Providing multiple passes will, however, enable anysuch larger deviations in position (or tool size) to be measured. Forexample, beam intensity data collected when the light beam moves fromthe fourth position 258 to the end position 260 would be able to measurethe edge of the dashed outline tool 266. It would, of course, also bepossible to use beam intensity data from different traverses of thelight beam if, for example, the tool was angled so different areas ofthe tool edge were present in different traverses of the light beam. Asan alternative to such a multi-pass technique, the width of the lightbeam could be increased.

The skilled person would appreciate that variations to the aboveembodiments are possible. For example, the method could be implementedusing non-contact tool setting apparatus mounted on any co-ordinatepositioning apparatus (e.g. a CMM, robot, off-line tool inspectionsystem etc) and not just a machine tool.

1. A method for assessing a profile of a tool using a non-contact toolsetting apparatus comprising a transmitter for emitting a light beam anda receiver for receiving the light beam, the receiver generating a beamintensity signal describing intensity of received light, the non-contacttool setting apparatus being mounted to a coordinate positioningapparatus that allows the tool to be moved relative to the non-contacttool setting apparatus, and the method comprising steps of: (i) usingthe coordinate positioning apparatus to move the tool relative to thenon-contact tool setting apparatus along a tool inspection pathcomprising a start position on an edge of the tool and an end positionon the edge of the tool, the end position being spaced apart from thestart position and the movement of the tool relative to the non-contacttool setting apparatus causing the light beam to be scanned along theedge of the tool from the start position to the end position without thetool moving out of the light beam; (ii) collecting beam intensity datadescribing the beam intensity signal that is generated by the receiveras the tool inspection path of step (i) is traversed, the beam intensitydata being collected for a plurality of positions that are spaced apartalong the edge of the tool between the start position and the endposition; and (iii) analysing the beam intensity data collected in step(ii) to determine a profile of the edge of the tool between the startposition and the end position.
 2. The method according to claim 1,wherein the tool inspection path is pre-calculated prior to step (i). 3.The method according to claim 1, wherein step (iii) comprises comparingthe beam intensity data collected in step (ii) with previously acquiredbeam intensity data.
 4. The method according to claim 3, wherein thepreviously acquired beam intensity data comprises data collected from aprevious measurement of the same tool or from a reference tool havingthe same nominal profile as the tool, and the analysis of step (iii)provides an indication of whether the tool profile has changed relativeto the previous measurement.
 5. The method according to claim 1, whereinthe tool is held in a rotatable spindle of the coordinate positioningapparatus, the tool comprises one or more cutting teeth located around aradius of the tool, and the tool is rotated about a longitudinal axis ofthe tool while the tool is moved along the tool inspection path.
 6. Themethod according to claim 5, wherein the one or more cutting teeth ofthe tool comprise a plurality of cutting teeth, and step (iii) comprisesidentifying minima and/or maxima associated with each tooth of theplurality of cutting teeth to separately assess the profile of eachtooth.
 7. The method according to claim 1, wherein the coordinatepositioning apparatus is a machine tool.
 8. A method for assessing aprofile of a tool using a non-contact tool setting apparatus comprisinga transmitter for emitting a light beam and a receiver for receiving thelight beam, the receiver generating a beam intensity signal describingintensity of received light, the non-contact tool setting apparatusbeing mounted to a coordinate positioning apparatus that allows the toolto be moved relative to the non-contact tool setting apparatus, and themethod comprising steps of: (i) using the coordinate positioningapparatus to move the tool relative to the non-contact tool settingapparatus along a tool inspection path comprising a start position onthe tool and an end position on the tool, the start position and the endposition being located at different positions along a longitudinal axisof the tool, and the movement of the tool relative to the non-contacttool setting apparatus causing the light beam to be scanned along thetool from the start position to the end position without the tool movingout of the light beam; (ii) collecting beam intensity data describingthe beam intensity signal that is generated by the receiver as the toolinspection path of step (i) is traversed, the beam intensity datathereby being collected for a plurality of positions that are spacedapart along the edge of the tool between the start position and the endposition; and (iii) analysing the beam intensity data collected in step(ii) to determine a profile of the edge of the tool between the startposition and the end position.
 9. The method according to claim 8,wherein the tool inspection path is pre-calculated prior to step (i).10. The method according to claim 8, wherein step (iii) comprisescomparing the beam intensity data collected in step (ii) with previouslyacquired beam intensity data.
 11. The method according to claim 10,wherein the previously acquired beam intensity data comprises datacollected from a previous measurement of the same tool or from areference tool having the same nominal profile as the tool, and theanalysis of step (iii) provides an indication of whether the toolprofile has changed relative to the previous measurement.
 12. The methodaccording to claim 8, wherein the tool is held in a rotatable spindle ofthe coordinate positioning apparatus, the tool comprises one or morecutting teeth located around a radius of the tool, and the tool isrotated about the longitudinal axis of the tool while the tool is movedalong the tool inspection path.
 13. The method according to claim 12,wherein the one or more cutting teeth of the tool comprise a pluralityof cutting teeth, and step (iii) comprises identifying minima and/ormaxima associated with each tooth of the plurality of cutting teeth toseparately assess the profile of each tooth.
 14. The method according toclaim 8, wherein the coordinate positioning apparatus is a machine tool.15. A method for assessing a profile of a non-rotating tool using anon-contact tool setting apparatus comprising a transmitter for emittinga light beam and a receiver for receiving the light beam, the receivergenerating a beam intensity signal describing intensity of receivedlight, the non-contact tool setting apparatus being mounted to acoordinate positioning apparatus that allows the non-rotating tool to betranslated along three mutually orthogonal linear axes relative to thenon-contact tool setting apparatus, and the method comprising steps of:(i) using the coordinate positioning apparatus to translate thenon-rotating tool relative to the non-contact tool setting apparatusalong one or more of the three mutually orthogonal linear axes so thatthe light beam is moved along an edge of the non-rotating tool; (ii)collecting beam intensity data describing the beam intensity signal thatis generated by the receiver while the light beam is moved along theedge of the non-rotating tool during step (i); and (iii) analysing thebeam intensity data collected in step (ii) to determine a profile of theedge of the tool.
 16. The method according to claim 15, wherein the toolinspection path is pre-calculated prior to step (i).
 17. The methodaccording to claim 15, wherein step (iii) comprises comparing the beamintensity data collected in step (ii) with previously acquired beamintensity data.
 18. The method according to claim 17, wherein thepreviously acquired beam intensity data comprises data collected from aprevious measurement of the same tool or from a reference tool havingthe same nominal profile as the tool, and the analysis of step (iii)provides an indication of whether the tool profile has changed relativeto the previous measurement.
 19. The method according to claim 15,wherein the coordinate positioning apparatus is a machine tool.
 20. Themethod according to claim 15, wherein step (ii) comprises digitising thebeam intensity signal to generate the beam intensity data, and step(iii) comprises using a digital signal processor to analyse the beamintensity data.